大葱提取物对微生物抑制作用的研究

以大肠杆菌、枯草芽孢杆菌、白色葡萄球菌、粘红酵母、黑曲霉为对象,研究了大葱的总提取物、蛋白成分、脂溶性成分及多糖成分的抑菌能力。结果表明,大葱总提取物对细菌和真菌均具有抑制作用,其中对白色葡萄球菌具有很强的抑制作用,对大肠杆菌和枯草芽孢杆菌也有一定的抑制作用,对粘红酵母黑曲霉也具有抑制能力;大葱脂溶性成分对细菌和真菌均具有抑制作用,大葱蛋白成分和多糖成分对细菌和真菌均没有抑制作用。研究表明,大葱中的抑菌成分主要为脂溶性成分。     

Differential hydrolysis of alk(en)yl cysteine sulphoxides by alliinase in onion macerates: flavour implications

Intact cells of Allium spp have no odour, but when cells are disrupted, the enzyme alliinase (EC 4.4.1.4) hydrolyses the S-alk(en)yl sulphoxides (ACSOs) to produce pyruvate, ammonia and the many volatile sulphur compounds associated with flavour and odour. In onions, there are three main sulphoxides: methyl, propyl and 1-propenyl, which gives rise to onion's tear-producing effect. The relative proportions of these are a factor in determining the subsequent flavour. γ-Glutamyl peptides, which are biosynthetic intermediates to ACSOs, are also present in significant amounts, but their contribution to flavour is not known. There is little work on the reaction of alliinase in vivo. The hydrolysis of ACSOs by alliinase was studied in rapidly macerated bulbs at intervals between 5 s and 2 h. ACSO and γ-glutamyl peptide levels were measured by HPLC, and pyruvate levels were measured spectrophotometrically. Although the hydrolysis of propenyl cysteine sulphoxide (PrenCSO) was immediate and almost 100% between 5 and 20 s after bulb maceration, the hydrolysis of propyl cysteine sulphoxide (PCSO) and methyl cysteine sulphoxide (MCSO) was incomplete. After 5 s maceration, about 50% PCSO and MCSO remained and thereafter no further hydrolysis occurred. The levels of ACSOs and the extent to which they were hydrolysed were dependent on the cultivar and sulphur environment in which it was grown. The addition of pyridoxal phosphate cofactor enhanced the extent of MCSO and PCSO hydrolysis. Additional purified alliinase per se had no effect. Substantial hydrolysis of γ-glutamyl peptides also occurred after maceration, and this was unexpected. Levels of pyruvate product were between 15 and 25% of the expected amount from ACSO hydrolysis assuming a stoichiometric relationship. The incomplete hydrolysis of MCSO and PCSO, enhancement of activity by additional pyridoxal phosphate and non-stoichiometric production of pyruvate are evidenced that reaction inhibition of alliinase may be occurring in onion macerates. © 1998 Society of Chemical Industry.     

DETERMINATION OF THE SOLUBLE IRON CONTENT OF FILTER AIDS: A COLLABORATIVE TRIAL

The international method for the determination of the soluble iron content of filter aids has been collaboratively tested by members of the Analysis Committee of the European Brewery Convention to obtain repeatability (r₉₈) and reproducibility (R₉₈) values. It was Judged that precision values were dependent on the quantity of the soluble iron content of the filter aids over the range 32 to 220 mg/kg. Repeatability (r₉₈) value of 0.050 m and reproducibility value (R₉₈) of 0.255 m were obtained over this range.     

32—THE SNARLING OF HIGHLY TWISTED MONOFILAMENTS. PART I: THE LOAD–ELONGATION BEHAVIOUR WITH NORMAL SNARLING

An account is given of an experimental investigation of the normal snarling of highly twisted monofilaments, those used being vulcanized rubber and nylon.

An earlier theoretical analysis is corrected, and the experimental results show that, after this correction, the theory put forward for the mechanical properties of the snarling mechanism holds reasonably well for elastic filaments. Although, as would be expected, there are larger deviations from the theory for viscoelastic filaments, the theory still gives a good indication of the behaviour of these filaments under torsion.     

33—THE SNARLING OF HIGHLY TWISTED MONOFILAMENTS. PART II: CYLINDRICAL SNARLING

An account is given of an experimental investigation of the cylindrical snarling of highly twisted monofilaments.

The theory underlying cylindrical snarling is set out, and an expression is derived for calculating the critical twist level at which normal snarling will be replaced by cylindrical snarling. Experiments on rubber filaments are described, and it is shown that there is good agreement between the theoretical and experimental results. Further experiments, in which the specimen was allowed to contract freely or forced into other forms, are also described.

It is shown from these experiments that it is difficult to establish the true equilibrium behaviour, since the situation appears to be dominated by frictional effects or by direct barriers to relative movement.